The present disclosure relates generally to methods and systems for location estimation, and more particularly, to methods and systems that estimate locations of mobile stations based on network-based and satellite-based signals.
Wireless location technologies have drawn a significant amount of attention over the past few decades. Different types of Location-Based Services (LBSs) have been proposed, including emergency 911 (E-911) subscriber safety services, location-based billing, navigation system, and applications for the Intelligent Transportation System (ITS). However, to meet all applications' needs, it is required to provide more accurate location estimation of a mobile device, such as a mobile phone, a smart phone, and a PDA under different environments.
A variety of wireless location techniques have been proposed. These techniques can be classified into network-based and satellite-based location schemes. The representative algorithms for the network-based location techniques are TDOA (Time Difference-Of-Arrival) and AOA (Angle-Of-Arrival) schemes. FIG. 1 is a schematic diagram illustrating a network-based architecture. In the TDOA scheme, a mobile station (MS) 110 receives signals coming from different wireless base stations (121, 122, and 123), and measures the time difference of the signals. In the AOA scheme, a home base station of the mobile station 110 observes the arrival angle of signals from the mobile station 110. On the other hand, the well-adapted technology for the satellite-based location method is GPS (Global Positioning System). FIG. 2 is a schematic diagram illustrating a satellite-based architecture. The mobile station 110 receives signals coming from a plurality of satellites (131 and 132), and measures TOA (Time-Of-Arrival) of the signals.
The performance of the location techniques, however, varies under different environments. For example, at rural areas, less base stations in a network-based system are installed, resulting in weak incoming signals or shortage of signal sources. Therefore, at rural areas, the network-based (i.e. TDOA, AOA) methods result in degraded performance for the location determination of mobile devices. On the other hand, the major problem for the satellite-based (i.e. GPS) method is that the performance considerably degrades when the satellite signals are severely blocked in urban valley areas.